Bobbin case tension spring



United States Patent [72] lnventors Ludwig J. Kuhar Clark; Joseph J. Dolney, Denville, New Jersey [21] Appl. No. 819,213 [22] Filed April 25, 1969 [45] Patented Sept. 29, 1970 [7 3] Assignee The Singer Company New York, New York a corporation of New Jersey [54] BOBBIN CASE TENSION SPRING I 5 Claims, 6 Drawing Figs.

[52] U.S.Cl 112/229 [51] Int. Cl. D05b 57/14 [50] Field of Search 1 12/229,

[56] References Cited UNITED STATES PATENTS 2,009,292 7/1935 Fleckenstein 1 12/230 9/1958 Spaine 2,851,977 112/231 3,087,388 4/1963 Kuhar.... 112/231X 3,381,642 5/1968 Bono 112/229 FOREIGN PATENTS 950,529 10/1956 Germany 112/229 Primary ExaminerAlfred R. Guest Attorneys-Marshall .1. Breen, Chester A. Williams, Jr., and

Robert E. Smith ABSTRACT: A bobbin case for use in a sewing machine comprising a cup-shaped body including a cylindrical outer wall and a substantially circular end face. A bobbin thread tension spring is adjustably secured to the outer wall. An overhanging arcuate lip projecting radially from the periphery of the end face overlays the spring to provide a smooth snag-free surface over which the needle thread loop can pass. A finger extends from an edge of the spring and folds over the spring to abut the lip thus preventing bobbin thread from becoming entrapped under the lip,

Patented Sept. 29, 1970 INVENTORS Ludwig J. Kuhor, BY Joseph J. Dolney j AT/'ORNEY Fig.6

BOBBIN CASE TENSION SPRING SUMMARY This invention relates to lock stitch sewing machines, and more particularly, to a bobbin case therefor.

In lock stitch sewing machines it is necessary to provide a bobbin case having a smooth snag free surface over which one limb of a needle thread loop can pass. Furthermore, it is conventional to provide a spring on the bobbin case cylindrical wall for applying proper tension to the bobbin thread. It had been found that when the loop taker manipulates a loop of thread the limb of the loop that passes over the bobbin case tends to snag on the spring or the spring securing screws. A solution to this problem provided an overhanging smooth arcuate lip projecting radially from the periphery of the bobbin end face to overlay the spring. Thus, the loop of needle thread smoothly glides over the lip onto the surface of the bobbin case face without becoming snagged on the spring or its securing means. It has been found, however, that the bobbin thread, when it is loose such as for instance prior to the making of the first stitch, can be carried down by the needle thread limb and tends to get trapped beneath the lip. One disadvantage of such trapping of the bobbin thread is that it may prevent the needle thread loop from drawing the bobbin thread into the work to form the stitch. This problem is amplified in cyclic sewing machines since the bobbin thread is cut at the end of each cycle and the cut end must be picked up by the loop of needle thread to make the first stitch of the following cycle. A second disadvantage of such trapping of the bobbin thread is that it can drastically change the tension which is applied to the bobbin thread thus causing a detrimental effect on the appearance of the stitching. It is, therefore, an object of this invention to provide in bobbin cases of this type a means for preventing entrapment of bobbin thread beneath the lip.

It is a more specific object of this invention to provide a bobbin case comprising a tension spring, an overhanging lip formed on the bobbin case to overlay the spring, and a finger extending from an edge of the spring and folding over the body of the spring to abut the lip so as to prevent bobbin thread from becoming trapped beneath the lip.

These and other objects will be apparent from the specification and claims which follow taken in connection with the accompanying drawings of a preferred embodiment in which:

FIG. 1 represents a front elevational view of a cyclic lock stitch sewing machine loop taker having a bobbin case of this invention and including portions of the sewing machine,

FIG. 2 is an enlarged exploded perspective view of the bobbin case of this invention prior to assembly of the spring and showing a fragmentary perspective of the thread carrying bobbin,

FIG. 3 is an enlarged perspective of the assembled bobbin case of this invention with the bobbin inserted and showing the position of the bobbin thread prior to the formation of the first stitch,

FIG. 4 is an enlarged side elevational view of the bobbin case,

FIG. 5 is an enlarged fragmentary cross-sectional view of the bobbin case taken substantially along line 5-5 of FIG. 4 and showing a portion of the finger in phantom, and

FIG. 6 is an enlarged fragmentary bottom plan view of the bobbin case.

The present invention illustrated in FIGS. 2-6 of the drawing will be explained as embodied in a cyclical lock stitch sewing machine of which FIG. 1 illustrates the stitch forming instrumentalities. Only those parts of the sewing machine and stitch forming instrumentalities which will aid in understanding this invention will be described herein. For a more detailed description reference may be had to US. Pat. Nos. 2,990,794 and 2,968,269.

Briefly, a rotary loop taker l cooperates with a reciprocating needle 2 to draw out a loop of needle thread N and to carry the needle thread loop about a mass of threadB stored on a bobbin 3 within a bobbin case 4 which bobbin case is supported in nonrotating relationship within the loop taker. The loop of needle thread is taken by the loop seizing beak 5 of the loop taker and passed around the bobbin case; the front limb 6 of the needle thread passing over the bobbin case. The bobbin thread is enclosed by the needle thread loop in the usual manner and when the needle thread loop is drawn up into a work fabric the bottom thread concatenated therewith is also drawn up and the stitch is tightened and set. At the end of the stitching operation in cyclic sewing machines, such as, for example, a buttonhole sewing machine, the threads are cut by a bobbin thread knife blade 7 cooperating with a ledger blade 8, as described in US. Pat. No. 2,968,269 supra, and a needle thread cutting mechanism (not shown) as is well known in the art. At the start of the following stitching cycle the loop of needle thread must pick up the loose cut end of the bobbin thread in order to sew the first stitch. Unless the needle thread loop picks up the bobbin thread, the first stitch, and no succeeding stitch can be properly set. If the bobbin thread should become caught on the surface of the bobbin case, it may not be long enough to be drawn to the work during the first stitch.

The bobbin case 4 of this invention comprises a cylindrical outer wall 9 and a circular end face 10, which together form a cup-shaped body of the bobbin case. Located on the face 10 is a pair of raised shoulders I1 and 12 which define a groove 13.

The upper surfaces of the shoulders are highly polished for purposes which will presently be made clear. Located in the groove 13 is a latch adapted to hold the bobbin case within the loop taker as is well known in the art.

As is customary, a flat thread tension leaf-spring 15 is provided on the cylindrical outer wall 9 so as to properly tension the bobbin thread passing through the bobbin case and between the forked end 16 of the spring. The spring includes two apertures 17 and 18 into which screws 19 and 20 respectively fit. The cylindrical wall 9 includes threaded apertures 21 and 22 which threadedly receive the screws 19 and 20, respectively, to secure the spring to the cylindrical wall. The tension applied by the spring can be adjusted by tightening or loosening the screw 20.

In order to provide a snag free surface over which a limb 6 of a needle thread loop may pass, there is provided on the bobbin case an overhanging lip 23 which is formed continuous with the end face 10 and projecting radially from the periphery thereof arcuately sloping toward the outer wall 9 to overlay a portion of the spring 15. The upper surface of the lip is highly polished to provide a smooth transitional surface for the passage of the limb 6 of needle thread from the loop taker onto the highly polished surface of the shoulders 11 and 12. The smoothly arcuate end of the lip ensures that the limb of needle thread will not snag on the spring as the limb rides onto the end face shoulders. The cutout 24 in the lip provides a clearance for insertion of a screwdriver to adjust screw 20.

Provided within the cup-shaped bobbin case on the bottom surface of the end face is an arbor 25 upon which the bobbin 3 is rotatable. The bobbin thread B passes within the case from the bobbin and then out through an aperture 26 beneath the spring 15. The thread is drawn along the cylindrical wall 9 between the fork 16 of the spring and over the hole 27, down through an aperture 28 into the case, and then up through an aperture 29. The threaded bobbin case is clearly shown in FIG. 3 with the bobbin thread shown positioned as it would be prior to a needle thread loop capturing it at the beginning of the first stitch of a stitching cycle.

It has been found that the bobbin thread in this position has a tendency to become trapped beneath the lip 23 and if this occurs the bobbin thread may not be long enough to be drawn up by the needle thread loop and carried to the work. To this end the present invention provides a finger 30 integral with the spring. The finger extends from the edge of the spring remote from the lip and folds or bends over the main body of the spring into abutting relationship with the lip. The tip 31 of the finger is of arcuate shape to conform to the contour of the lip so as to prevent any protrusions thereof from interfering with the needle thread as it rides across the lip. It can be clearly seen that the finger closes off the path of the bobbin thread to beneath the lip and thus prevents the entrapment problem. The bobbin thread passes over the upper surface of the finger and is available to be drawn up to the work by the needle thread loop.

We claim:

1. A bobbin case having a cup-shaped body comprising a cylindrical outer wall and a substantially circular end face, a thread tension leaf-spring secured to the outer surface of the outer wall and contiguous with a portion thereof, a lip formed on the periphery of the end face overlaying the spring, and a finger extending from the edge of the spring opposite said lip and folded over the main body thereof into abutting relationship with said lip.

2. The bobbin case as defined in claim 1 wherein the lip comprises an arcuate projection extending radially from the periphery of the end face to overlay the spring, the lip being formed to provide a smooth transition with the end face ad jacent the periphery.

3. The bobbin case as defined in claim 2 wherein said finger is integral with the spring, the finger having an arcuately shaped tip which conforms to the contour of the lip, the tip of the finger abutting the lip to provide a continuation thereof.

4. A bobbin case for use in a two thread lock stitch sewing machine having a loop taker comprising a cup-shaped body including a cylindrical outer wall and a substantially circular end face, a bobbin thread tension spring adjustably secured to the outer surface of the outer wall, means for adjustably securing the spring to said wall, an overhanging lip formed continuous with said end face projecting radially from the periphery thereof and sloping toward said wall, said lip overlaying the spring to provide a smooth transitional surface for the passage of needle thread from the loop taker onto the surface of the end face, and means on the spring for preventing entrapment of bobbin thread beneath the overhanging lip. i

5. The bobbin case as defined in claim 4 wherein said means for preventing entrapment comprises a finger integral with the spring extending from the edge thereof opposite said lip and folded over the body of the spring to abut the lip. 

